A focal seizure, historically known as a partial seizure, is an episode of abnormal electrical discharge originating within a limited area of one hemisphere of the brain. This localized nature distinguishes it from a generalized seizure, which involves both sides of the brain from the onset. Clinicians now primarily use “focal seizure” to describe this event, reflecting a precise understanding of where the electrical activity begins. The specific symptoms experienced are directly related to the brain region where this disturbance is occurring, whether it controls movement, sensation, or emotion.
Classification of Focal Seizures
The current classification of focal seizures is based on the patient’s level of awareness during the event. The first category is the Focal Aware Seizure, previously known as a simple partial seizure. During this seizure, the individual remains fully conscious and alert, able to recall the event and interact with their environment.
These aware seizures are typically very brief, often lasting only a few seconds up to a minute or two, and consciousness is preserved because the electrical activity remains confined to a small brain area. The second category is the Focal Impaired Awareness Seizure, formerly called a complex partial seizure. In this instance, the seizure activity affects areas of the brain responsible for maintaining alertness and responsiveness.
Although the person may not fall unconscious, their awareness is significantly altered, resulting in a dazed or confused state. They may be unable to respond appropriately to their surroundings and often have no memory of the seizure afterward. Any decrease in awareness classifies the event into this impaired awareness category, reflecting a temporary disruption of normal cognitive function.
Recognizing the Signs and Symptoms
The manifestations of a focal seizure are diverse because the symptoms correspond directly to the specific brain region where the abnormal electrical activity is occurring. When the seizure begins in the motor cortex of the frontal lobe, symptoms may include rhythmic twitching or jerking of a limb or the face on the opposite side of the body. These movements can sometimes spread sequentially, a phenomenon described as a Jacksonian march.
Seizures starting in the temporal lobe often produce non-motor symptoms, including emotional or psychic disturbances. Individuals may experience intense fear or panic, déjà vu, or auditory hallucinations. Autonomic symptoms involving involuntary bodily functions can also arise, such as a sudden racing heart, stomach upset, or changes in skin color, due to the involvement of brain areas controlling internal organs.
Sensory symptoms are common when the seizure involves the parietal or occipital lobes, resulting in abnormal sensations like localized tingling or numbness, or visual disturbances. In cases of focal impaired awareness seizures, the person may exhibit automatisms, which are repetitive, non-purposeful behaviors:
- Lip smacking.
- Chewing.
- Picking at clothes.
- Aimlessly walking.
The specific combination of signs provides clues to the neurologist about the precise point of origin within the brain.
Identifying Underlying Causes and Diagnosis
A focal seizure is the result of an underlying condition that has created a localized area of hyperexcitable nerve cells in the brain. Structural abnormalities are a frequent cause, which can include brain tumors, scarring left behind by a previous stroke, or damage from a traumatic brain injury. Infections such as meningitis or encephalitis can also leave behind scar tissue that triggers abnormal electrical activity.
In some cases, the cause is a developmental abnormality that occurred before birth, such as focal cortical dysplasia, where the brain tissue is abnormally formed. While many cases of focal seizures are linked to these structural issues, a significant number of individuals do not have a clear, known cause. For those over the age of 65, vascular disease leading to small strokes is a common factor.
The diagnostic process begins with a detailed patient history, often relying on eyewitness accounts of the seizure event to understand the specific symptoms and their sequence. To confirm the diagnosis, a physician will order an electroencephalogram (EEG). This test records the brain’s electrical patterns and can reveal characteristic spikes or waves that indicate the seizure activity originates.
Imaging tests are also routinely used to search for structural causes of the seizure focus. A magnetic resonance imaging (MRI) scan provides detailed pictures of the brain tissue, allowing doctors to identify tumors, stroke lesions, or areas of scarring. Sometimes a computed tomography (CT) scan is used, though MRI is generally preferred for its superior detail in soft tissues, guiding treatment decisions.